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Within the bustling cityscape, an often overlooked environmental injustice is impacting the lives of marginalized urban communities. Residents already grappling with heightened air and water pollution and scarce greenspaces find themselves contending with another challenge—noise pollution. The rumble of industrial activities, the roar of highways, and the thunder of airports converge to create a cacophony disproportionately affecting those on the fringes. Noise isn't just a concern for humans—it also elicits a range of impacts to wildlife. With hundreds of studies documenting the effects on terrestrial and aquatic species, noise pollution emerges as a powerful but often invisible force impacting wildlife behavior and ecology.

Enter systemic biases, the architects of urban inequality. These biases continue to shape the very fabric of institutional policies and urban planning practices, fueled by the historical and socio-economic factors, particularly residential segregation. The result? An uneven distribution of environmental hazards, where pollution prevails, and benefits, like precious greenspaces, are scarce. One prime example of this is the enduring legacy of redlining in the United States. Between 1933 and 1968, the Home Owners’ Loan Corporation (HOLC) graded neighborhoods in U.S. cities from A to D, with lines drawn based on race dictating the fate of entire communities. Areas predominantly inhabited by people of color and immigrants found themselves relegated to C and D grades, receiving minimal investments from governments and banks. This is no longer an explicit practice, but it was never redressed, and social and ecological imprints remain.

In redlined neighborhoods, where noise combines with limited green spaces and other environmental disparities, the result might be a double blow to wildlife and people. Yet, our grasp of how noise spreads across redlining grades and its potential human and wildlife repercussions are yet to be fully appreciated.

Our study aims to address this critical knowledge gap by focusing on the undeniable link between redlining outcomes and racial bias. This research considers the intersectionality of noise pollution, social justice, and wildlife biology, revealing how inequitable distributions of noise associated with redlining affects both the urban landscape and its human and wildlife inhabitants.

What inspired this work?

Our study was inspired by Christopher Schell et al.’s (2020) paper that highlights how structural inequality and racist practices can have cascading impacts on urban biological diversity. Shortly after their paper was published, several authors from our team met to discuss ideas for a potential lab paper. Several of us rely on acoustic recordings or listening activities (e.g., bird point counts, bat/elephant recordings) to study wildlife across varied landscapes, and we wondered how urban noise might affect wildlife distributions and behaviors. We were familiar with some of the ecological consequences of noisy environments (e.g., the phantom road experiment) and agreed that a spatial analysis of noise could help us assess its varying impacts for urban human and wildlife communities.

What did we do? 

Our interdisciplinary team investigated whether noise was inequitably distributed across redlining grades using a spatial analysis of noise across 83 U.S. cities, and explored what the consequences of inequitable noise might be for urban wildlife using a literature review. We originally intended to analyze ecological data concerning the impact of noise on wildlife rather than conducting a literature review. However, ecological data in redlined communities are also underrepresented due to historic biases, making such an analysis challenging.

What did we find?

Our research shows a clear signal of inequitable noise exposure. Across 83 U.S. cities, grade D neighborhoods had over 10 times higher maximum noise levels than Grade A neighborhoods, and HOLC grades predicted urban noise pollution more than population size. Notably, grade D neighborhoods often exceeded 90 dB noise levels known to cause hearing damage, physical pain, and sociopsychological stress in humans, while grade A neighborhoods almost always had maximum noise levels below this limit. Moreover, grade A neighborhoods frequently had maximum noise levels below 70 dB, the EPA’s recommended upper noise limit to avoid human health impacts, while grade D neighborhoods were almost always above this 70 dB limit. 

Our review further suggests that inequitable noise can impact urban wildlife. We found that as noise exposure increases to 90 dB+ (levels more commonly found in redlined neighborhoods), the biological effects on urban wildlife intensify, leading to altered behavior and physiology, fitness consequences, and population declines across a variety of taxa. For example, 72% of population-level studies reported reduced wildlife abundance and 93% of vocalization studies observed changes in vocal behavior, particularly in urban birds.

 These results emphasize the need for equitable urban planning, particularly in historically redlined neighborhoods that also face challenges in accessing green spaces. Exposure to natural sounds and biodiverse greenspaces is linked to improved human health. Thus, addressing noise pollution, along with increasing green infrastructure, can amplify restorative impacts, potentially leading to increased biodiversity and well-being for both wildlife and humans. 

A call to action

Several U.S. cities are now recognizing their responsibility in addressing environmental injustice by increasing access to parks and green spaces for marginalized communities. However, there is also a pressing need to incorporate noise mitigation measures alongside green infrastructure improvements to ensure that both wildlife and people can enjoy the benefits of additional green infrastructure without the negative impacts of noise. 

The good news is that the tools and actions needed to address noise inequities already exist. Urban planners can implement zoning policies targeting noise reduction (e.g., traffic speed reductions/monitoring and regulation of industrial activities and noisy infrastructure). Planners can also weave tree lines and lush borders into the urban tapestry, absorbing and dialing down the noise, and can integrate smart city technologies like sensors and data analytics to identify noise hotspots, along with noise barriers, quiet pavement technologies, and noise-absorbing materials in public spaces. These actions should include residents in the planning process. Residents can also wield the power to curb urban noise by opting for quieter transportation like walking or cycling when possible, engaging in community advocacy and participating in local government meetings to raise awareness about noise pollution, and supporting candidates and policies focused on environmental justice.

Our study also underscores the imperative for the wider scientific community to actively explore the impact of systemic racism on biological patterns and processes. Recognizing and confronting systemic racism is crucial to prevent research biases, empower researchers to dismantle unjust structures, and lay the groundwork for advocating for policies that foster truly equitable systems.

Diverse and multidisciplinary teams enhance scientific understanding

We leveraged a blend of our disciplines, passions, and unique perspectives to craft this study, aiming to advance knowledge in urban ecology with a justice-centered approach. Our team comprises scientists with diverse identities and interests, including graduate students, postdoctoral researchers, and faculty with expertise in acoustic ecology, urban ecology, community-centered ecology, social justice, racial equity, human-wildlife interactions, and more. Members of our team encompass various intersecting identities, such as neurodiverse, LGBTQIA+, people of color, multi-national, first-generation, and non-traditional scientists. These perspectives help to contextualize the study and bring in diverse lenses. The lived experiences and understandings of these scholars enriched how we conceptualized and executed the study, contributing to a holistic scientific understanding.